The present invention relates to a discharge lamp lighting apparatus and, more particularly, to an improvement in such an apparatus as accomplished by the use of semiconductor devices.
Various discharge lamp lighting circuits have been developed in recent years employing solid state circuits. One such apparatus is described and claimed in U.S. Pat. No. 3,753,037, entitled "DISCHARGE-LAMP OPERATING DEVICE USING THYRISTOR OSCILLATING CIRCUIT," issued Aug. 14, 1973, and assigned to New Nippon Electric Company Ltd.
The apparatus described in the aforementioned patent has some distinct advantages obtained by the use of a thyristor type voltage-responsive switching element such as a (SSS) Silicon Symmetrical Swtich, a (SCR) Silicon Controlled Rectifier, TRIAC or a bi-directional two-terminal diode thyristor, and comprises an oscillator which is implemented by a first oscillation circuit having a power source, a linear inductor and a capacitor connected in series, a second oscillation circuit connected across the capacitor and having a bounce or back swing booster inductor and a voltage-responsive switching element connected to series, and a third oscillation circuit comprising the bounce booster inductor and its distributed capacity, as well as a discharge lamp connected across the capacitor. An oscillation voltage generated across the capacitor is sufficiently high to start or ignite the discharge lamp. As a power source a d.c. or an a.c. source may be employed. Where the discharge lamp is a hot-cathode discharge lamp which has a pair of filaments serving as discharge electrodes, the filaments are generally connected in series with the first oscillation circuit and/or with the second oscillation circuit for the purpose of heating the filaments in a quick manner. As will be described in more detail hereinafter, the maximum instantaneous value of the output voltage of the power source is larger than the braekdown voltage of the switching element apart from a spike pulse or voltage. As a result, the high oscillation voltage generated across the capacitor causes the discharge lamp to be started or ignited, and then the oscillation is stopped and a stabilized discharge operation is maintained thereafter.
In the prior art certain problems have been encountered, for example, in connection with the starting of discharge lamps under different temperature conditions, especially under high and low temperatures. Further, so called half-wave lighting frequently occuring in worn out lamps may also occur prior to the end of the useful life of a lamp and this is to be avoided. These problems will be described in more detail below.